sun.nio.ch.Util: Don't cache an unlimited amount of memory

[Alan Bateman]

On 12/01/2016 15:19, Tony Printezis wrote:
> Alan and all,
>
> Here’s the first version of this patch (along with a test):
>
> http://cr.openjdk.java.net/~tonyp/nio-max-buffer-size/webrev.1/ 
> <http://cr.openjdk.java.net/%7Etonyp/nio-max-buffer-size/webrev.1/>
>
> A few points:
>
> * I called the property java.nio.MaxCachedTempBufferSize. I’m happy to 
> call it something else if you don’t like the name.
>
> * I was not sure what the best way to read the property is. I took the 
> same approach used for MaxDirectMemorySize and I read it from the 
> saved properties on sun.misc.VM. Feel free to suggest a more 
> appropriate alternative.
>
> * I have compiled and run the test and it works as expected. But I 
> haven’t run it within jtreg, though, given that I need to upgrade my 
> jtreg to a more recent version. I’ll do that when I get a chance. But 
> some tweaking on the metadata on the top comment might be required…
>
>
The property is JDK-specific so better to use jdk.* as prefix. A name 
such as jdk.nio.maxCachedBufferSize works for me. If it's property only 
then we'll need to get the value from System.getProperty and that will 
need to be done in a privileged block.

It would be good if maxCachedBufferSize could be final. Also as this is 
a static then the isTempBufferTooLarge methods could be static too. That 
would be arguably cleaner anyway as the limit is not specific to the 
thread's buffer cache. It would also mean that getTemporaryDirectBuffer 
and offeXXXTemporaryDirectBuffer can just check the size without needing 
the thread's cache.

The test will need a bit of clean-up. I assume you will add a copyright 
header.  It would be good to use try-with-resources as a disk full or 
other issue will leave the file open. There are really long (>200 chars) 
lines that are really hard to look at without scrolling so it would be 
good to get those down to sane lengths that would allow for future 
side-by-side diffs.

Otherwise the approach seems okay to me.

-Alan






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